Process for maintaining the clarity of photographic silver halide emulsions at relatively high developer temperatures



arr-mime The invention is concerned with a process for improving theclarity of, photognaphic silver halide emulsions during development atrelatively high temperatures. Photognaphiesilver halide emulsions have atendency at relatively high developer temperatures to give aconsiderable degree of fogging which appreciably impairs the quality ofthe picture. Since relatively high developer temperaturesfrequentlycannot be avoided, because of unfiavorable climaticconditions, it has long been desired to prevent the formation of thisdevelopment fog by adding suitable substances to thephotographic silverhalide emulsion, to the photographic auxiliary layers, or to theprocessing baths.

A number of substances have also been described which have the effect ofkeeping the unexposed silver halide clear, but these influencedisadvantageously other photographic properties in one way or another.The most important of these substances include benztriazole, whichsubstantially prevents fog formation, but simultaneously shifts the toneof the image undesinably towards blue-black. The use of urea and itssubstitution products as fog inhibitors is described in U.S. Patent No.1,763 ,990. However, these tog inhibitors are not able to prevent thedevelopment of fog. which occurs at relatively high developertemperatures.

It has now been found that the flog formation at relatively highdeveloper temperatures can largely be prevented if, to the photographicsilver halide emulsion or photographic auxiliary layers, such asprotective or intermediate layers or the like, are added, prior to thecasting, substituted 4(5)-aminobenztriazoles of the following generalformula:

in which R represents an aliphatic radical with at least two carbonatoms, an aromatic or heterocyclic radical which in turn may besubstituted, and X represents a simple chemical bond, an oxygen atom oran imino radical and in which the benzene nucleus may also carry othersubstituents.

Suitable substances for this purpose that conform to the foregoingformula are acylated aminobenztriazoles, such asS-benzoylaniinobenztriazole, carbamic acid derivatives such asScarbethoxyaminobenztriazole, S-carbophenoxyaminobenztriazole,4-carbophenoxyaminobenztriazole, 4carbophenoxyam-ino-6eaminobenztriazlole and urea derivatives ofbenztriazole, such as N-'ethyl-N-(5)- benztriazolyl urea,N-pheny1-N-(4)-benztriazolyl urea, N-phenyl-N-()-benztriazolyl urea,N-(4'-ethoxyphenyl) N-(5)-benztriazolyl urea, N-(3-ch1orphenyl)-N- (5-benztriazolyl urea, N- 4'-chlorphenyl) N-(5 -benztr-iazolyl urea.

The preparation of these compounds may be 'eifected by known methods.

, The acylated aminobenztriazoles are obtained by reac- Sttes Ptent liceH G CH3 N S H 02 The outstanding efficacy of the substances according tothe invention is apparent from the following table, which reproduces thefog values of a silver bromide emulsion according to Bios Final ReportNo. 252, which emulsion had been cast with and without addition ofaminobenztriazole derivatives, after development for 4 minutes at 30 C.

- Fog density after develop- Silver bromide emulsion: ment at 30 C.

Without additive 0.052. With N-ethyl-N-(5)-benztriazo1yl urea (Example2) 0.031

With N-phenyl-N'-(4) -benztriazolyl urea 0.009 WithN-phenyl-N'-(5)-benztriazolyl urea 0.015 With N (4-ethoxyphenyl)-N'-(5)-benztriazolyl urea 0.015 With N-( 3-chlorphenyl -N-( 5 -benztriazolylurea 0.017 With N-(4'-chlorpheny-l) -N'-(5 -benztriazolyl urea, 0.009With S-benzoylaminobenztriazole (Example 1) 0.038 WithS-carbophenoxyaminobenztriazole 0.017 With4carbophenoxyaminobenztriazole 0.033 With 4carbophenoxyarnino-flaminobenztriazole 0.027 With4-benzoylaminobenztriazole 0.041 With 5-carboethoxyaminobenztriazole0.037

1 This compound is also referred to as i ('3-phenyl-ureido)-1,2,3-henzotriazole. I

If N-phenyl-N'-(5)-benztriaziolyl urea is added to a protective layer,the fog value after development for 4 minutes at 30 C. is 0.045, whereasthe fog value without adding the stabilizer increases to 0.195. Theemulsion used for this test was the same as mentioned above but thisbatch was very susceptible to fog formation.

The substances according to the invention may be used in quantities from5 to 250 mg. per liter of emulsion. 1 liter of emulsion containsapproximately 30 g. of silver halide.

'Ihe substances according to the invention are suitable for reducing thefogging of silver chloride, silver bromochloride and silver bromideemulsions, and the maximum eiiect is produced with silverbnomide-ammonia emulsions. The emulsions may contain up to 5 percentsilver iodide.

Example 1 A silver bromide emulsion containing g. of AgBr to 3 litershas added thereto 8 cc. per liter of a 1% solution of the compound Afteradding the other conventional hardening agents, the emulsion is cast onto paper.

The fog value with and without addition of stabilizer, after 4 minutesdevelopment at 30 C., are set out in the foregoing table. Development iscarried out in a conventional metol-hydroquinone developer which is madealkaline with soda.

Example 2 A silver bromochloride emulsion containing about 35 g. of AgBrand 70 g. of AgCl to three liters has added thereto, 3 cc. per liter ofa 1 percent solution of the compound:

and the emulsion is cast after addition of other hardening agents.

When the stabilizer is added the fog value after development for 4minutes is 0.015 whereas it is 0.124 when no stabilizer has been added.

Example 3 The stabilizer of the formula was prepared as follows:

4 grams of S-aminobenztriazole and 5.2 grams of the hydrochloride ofisonicotinic acid chloride are refluxed for 3 hours in 50 cm. ofpyridine. The reaction mixture was precipitated by addition of water,filtered and recrystallized from dimethylformamide. The product melts at3 3 8 C. under decomposition.

50 mg. of the above-mentioned compound were added to 1 liter of a silverbromide emulsion according to Bios Final Report No. 252. The developmentis achieved in the conventional metal-hydroquinone developer which ismade alkaline with soda. After 4 minutes developing at 30 C. the fogvalue without addition of stabilizer was 0.141 while in the presence ofthe above-mentioned stabilizer the fog value was only 0.117. The batchof the above-mentioned silver bromide emulsion was very susceptible tofog formation.

Example 4 The stabilizer of the formula velopment was accomplished asdescribed in the foregoing example. After 4 minutes developing at 30 C.the fog value without addition of stabilizer was 0.113 while in thepresence of the stabilizer of the above-mentioned formula the fog valuewas only 0.076.

Example 5 The stabilizer of the formula H o d NH (3 NH 2 I N H2C\ /CH2 sO: H

was prepared by reaction of cyclo-tetra-methylene sulfoneisocyanate with5 amino-benztriazole. Development was carried out as described inExample 4. The fog value without addition of the stabilizer was 0.113.The fog value was reduced by this stabilizer to 0.06.

It is to be understood that the stabilizers according to the inventionmay be substituted by various groups, for example the followingcompounds are suitable stabilizers:

prepared by reaction of butyrolactone with 5-amino-benztriazole;

prepared by reaction of a chloro-substituted fatty acid ester withS-amino-benztriazole;

0 o N mo-ii-oHr-d-NH- prepared by reaction of acetoacetic ester withS-arninobenztriazole;

prepared by reaction of a chloro-substituted alkylene isocyanate withS-amino-benztriazole;

prepared by reaction of alphanaphthyl isocyanate withS-amino-benztriazole.

What is claimed is:

1. A photographic material which comprises a lightsensitive silverhalide emulsion layer and a contiguous auxiliary layer, at least one ofwhich layers contains a derivative of amino-'benztriazole selected fromthose having the following general formulae:

in which R represents a radical selected from the class consisting ofalkyl with at least 2 carbon atoms, substituted alkyl with at least 2carbon atoms, aryl, substi tuted aryl, heterocyclics and substitutedheterocyclics; X

6 being a member selected from the group consisting ot a simple chemicalbond, an oxygen atom, and an iminc radical, in an amount sufificient toinhibit the formatior of fog in the subsequent development of the silverhalide emulsion layer of the said photographic material at 2 relativelyhigh development temperature.

2. A photographic material as defined in claim 1, the light-sensitivesilver halide emulsion layer of which con tains an aminobenztriazolederivative as defined it claim 1.

3. The photographic material as defined in claim 1 the contiguousphotographic auxiliary layer of which contains the amino-b'enztriazolederivative as defined i1 claim 1.

4. A photographic material as defined in claim 1, the silver halideemulsion layer of which contains 4-(3-phen' ylureido) 1,2,3 -benzotriazole.

References Cited in the file of this patent FOREIGN PATENTS 350,996Great Britain June 19, 1931

1. A PHOTOGRAPHIC MATERIAL WHICH COMPRISES A LIGHTSENSITIVE SILVERHALIDE EMULSION LAYER AND A CONTIGUOUS AUXILIARY LAYER, AT LEAST ONE OFWHICH LAYERS CONTAINS A DERIVATIVE OF AMINO-BENTRIAZOLE SELECTED FROMTHOSE HAVING THE FOLLOWING GENERAL FORMULAE: